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<html><head>
<title>XLISP reader</title>
<style type="text/css">
.example {
color: #000000;
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<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
<hr>
<h1>Reader</h1>
<hr>
<hr>
<h2>read-from-string</h2>
<hr>
<pre class="example">
(defun <font color="#0000CC">read-from-string</font> (string)
(read (make-string-input-stream string)))
</pre>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="global-readtable"></a>
<hr>
<h2>*readtable*</h2>
<hr>
<p>The <a href="../reference/global-readtable.htm">*readtable*</a> system
variable contains the reader table array. <nobr>The table</nobr> is
<nobr>128 entries</nobr> <nobr>[0..127]</nobr> for each of the
<nobr>7-bit</nobr> ASCII characters that XLISP
<nobr>can <a href="../reference/read.htm">read</a></nobr>.</p>
<ul>
<li><nobr><a href="../reference/read.htm">read</a> - function to read a lisp expression</nobr></li>
<li><nobr><a href="../reference/global-readtable.htm">*readtable*</a> - system variable, holding the readtable</nobr></li>
<ul>
<li><nobr><a href="../reference/nil.htm">NIL</a> - invalid character</nobr></li>
<li><nobr><a href="../reference/keyword-constituent.htm">:constituent</a> - symbol constituent</nobr></li>
<li><nobr><a href="../reference/keyword-sescape.htm">:sescape</a> - whitespace character</nobr></li>
<li><nobr><a href="../reference/keyword-mescape.htm">:mescape</a> - multiple escape character</nobr></li>
<li><nobr><a href="../reference/keyword-white-space.htm">:white-space</a> - single escape character</nobr></li>
<li><nobr><a href="../reference/keyword-tmacro.htm">:tmacro</a> - terminating readmacro</nobr></li>
<li><nobr><a href="../reference/keyword-nmacro.htm">:nmacro</a> - non-terminating readmacro</nobr></li>
</ul>
</ul>
<p>See also the
<nobr><a href="../manual/xlisp.htm#lexical-conventions">Lexical Conventions</a></nobr>
and <a href="../manual/xlisp.htm#the-readtable">Readtable</a> sections in the
<nobr>XLISP 2.0</nobr> manual.</p>
<a name="print-readtable"></a>
<hr>
<h2>print-readtable</h2>
<hr>
<pre class="example">
(defun <font color="#0000CC">print-readtable</font> ()
(dotimes (index 128)
(format t <font color="#880000">"ASCII-~a ~a = ~a~%"</font>
(cond ((<= 0 index 9) (format nil "00~a" index))
((<= 10 index 99) (format nil "0~a" index))
(t index))
(if (< 31 index 127)
(code-char index)
(case index
(0 "[null] ")
(1 "[start of heading] ")
(2 "[start of text] ")
(3 "[end of text] ")
(4 "[end of transmission] ")
(5 "[enquiry] ")
(6 "[acknowledge] ")
(7 "[terminal bell] ")
(8 "[backspace] ")
(9 "[horizontal tab] ")
(10 "[line feed] ")
(11 "[vertical tab] ")
(12 "[form feed] ")
(13 "[carriage return] ")
(14 "[shift out] ")
(15 "[shift in] ")
(16 "[data link escape] ")
(17 "[device control 1, xon] ")
(18 "[device control 2] ")
(19 "[device control 3, xoff]")
(20 "[device control 4] ")
(21 "[negative acknowledge] ")
(22 "[synchronous idle] ")
(23 "[end transmission block]")
(24 "[cancel line] ")
(25 "[end of medium] ")
(26 "[substitute] ")
(27 "[escape] ")
(28 "[file separator] ")
(29 "[group separator] ")
(30 "[record separator] ")
(31 "[unit separator] ")
(127 "[delete]")))
(aref <font color="#AA5500">*readtable*</font> index))))
</pre>
<hr>
<h2>get-macro-character</h2>
<hr>
<p><div class="box">
<dl>
<dt>(<b>get-macro-character</b> <i>char</i>)</dt>
<dd><i>char</i> - a character<br>
returns - the code associated with the
<a href="../reference/global-readtable.htm">*readtable*</a> entry or
<a href="../reference/nil.htm">NIL</a></dd>
</dl>
</div></p>
<pre class="example">
(defun <font color="#0000CC">get-macro-character</font> (char)
(if (consp (aref <font color="#AA5500">*readtable*</font> (char-code char)))
(cdr (aref <font color="#AA5500">*readtable*</font> (char-int char)))
nil))
</pre>
<p> The '<nobr>get-macro-character</nobr>' function returns the code that
will be executed when the specified character 'char' is encountered by the
XLISP reader.</p>
<p>The 'get-macro-character' function will return a
<a href="../reference/nil.htm">NIL</a> value if the table entry is
<nobr><a href="../reference/nil.htm">NIL</a> ,</nobr>
<nobr><a href="../reference/keyword-constituent.htm">:constituent</a> ,</nobr>
<nobr><a href="../reference/keyword-sescape.htm">:sescape</a> ,</nobr>
<a href="../reference/keyword-mescape.htm">:mescape</a> or
<a href="../reference/keyword-white-space.htm">:white-space</a>. If the table entry is
<a href="../reference/keyword-tmacro.htm">:tmacro</a> or
<nobr><a href="../reference/keyword-nmacro.htm">:nmacro</a> ,</nobr> then the code
associated with the entry is returned.
<a href="../reference/keyword-tmacro.htm">:tmacro</a> is used for a terminating
read-macro. <a href="../reference/keyword-nmacro.htm">:nmacro</a> is used for a
non-terminating read-macro. 'get-macro-character' does not differentiate
whether the code returned is a
<a href="../reference/keyword-tmacro.htm">:tmacro</a> or an
<a href="../reference/keyword-nmacro.htm">:nmacro</a>.</p>
<p>The function returned may be a built-in read-macro function or a user
defined <a href="../reference/lambda.htm">lambda</a> expression. The function
takes two parameters, an input stream specification, and an integer that is
the character value. The function should return
<a href="../reference/nil.htm">NIL</a> if the character is 'white-space' or a
value <a href="../reference/cons.htm">cons</a>ed with
<a href="../reference/nil.htm">NIL</a> to return the value.</p>
<p>Examples:</p>
<pre class="example">
(get-macro-character #\() => #<Subr-(null): #...></font>
(get-macro-character #\#) => #<Subr-(null): #...></font>
(get-macro-character #\Space) => NIL</font>
</pre>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
<a name="set-macro-character"></a>
<hr>
<h2>set-macro-character</h2>
<hr>
<p><div class="box">
<dl>
<dt>(<b>set-macro-character</b> <i>char function</i> [<i>termination-flag</i>])</dt>
<dd><i>char</i> - a character expression<br>
<i>function</i> - a function definition<br>
<i>termination-flag</i> - an expression, <a href="../reference/nil.htm">NIL</a> or
non-<a href="../reference/nil.htm">NIL</a><br>
returns - always returns <a href="../reference/t.htm"> T </a></dd>
</dl>
</div></p>
<pre class="example">
(defun <font color="#0000CC">set-macro-character</font> (char function &optional terminate-p)
(setf (aref <font color="#AA5500">*readtable*</font> (char-code char))
(cons (if terminate-p :tmacro :nmacro) function))
t)
</pre>
<p>The '<nobr>set-macro-character</nobr>' function installs the code that
will be executed when the specified character 'char' is encountered by the
XLISP reader.</p>
<p>The 'set-macro-character' function only allows you to put in a
terminating read-macro function <a href="../reference/keyword-tmacro.htm">:tmacro</a> or
a non-terminating read-macro-function
<a href="../reference/keyword-nmacro.htm">:nmacro</a>. If the 'termflag' is present and
non-<nobr><a href="../reference/nil.htm">NIL</a> ,</nobr> then the 'function'
will be put in <a href="../reference/global-readtable.htm">*readtable*</a> as a
<a href="../reference/keyword-tmacro.htm">:tmacro</a> entry. If 'termflag' is not present
or <nobr><a href="../reference/nil.htm">NIL</a> ,</nobr> then 'function' will
be put in <a href="../reference/global-readtable.htm">*readtable*</a> as a
<a href="../reference/keyword-nmacro.htm">:nmacro</a> entry. The 'function' can be a
built-in read-macro function or a user defined
<a href="../reference/defun.htm">defun</a> symbol or a
<a href="../reference/lambda.htm">lambda</a> expression.</p>
<p>The 'function' takes two parameters, an input stream specification, and
an integer that is the character value. The 'function' should return
<a href="../reference/nil.htm">NIL</a> if the character is 'white-space' or a
value <a href="../reference/cons.htm">cons</a>ed with
<a href="../reference/nil.htm">NIL</a> to return the value. The function
'set-macro-character' always returns
<a href="../reference/t.htm"> T </a>.</p>
<p>Examples:</p>
<pre class="example">
> (print "hi") % comment
"hi"
"hi"
<font color="#AA0000">error: unbound variable - %</font> <font color="#008844">; % is interpreted as a variable</font>
> (setq readtable-backup *readtable*)
#( ... very-long-value ... )
> (set-macro-character #\% (get-macro-character #\;) t)
T
> (print "hi") % comment
"hi" <font color="#008844">; no error because</font>
"hi" <font color="#008844">; % is now a comment character</font>
> (setq *readtable* readtable-backup)
#( ... very-long-value ... )
</pre>
<p><b>Important:</b> before manipulating the XLISP
<a href="../reference/global-readtable.htm">*readtable*</a> it's always a
good idea to store the original contents in some other variable.</p>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
<hr>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
</body></html>
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